The movement of goods, materials and workpieces and people within and about factory and warehousing environments typically is carried out by relatively small, dedicated transport vehicles such as forklift trucks and the like. Operators of these in-plant vehicles have been observed to exhibit an incentive based tendency to operate them at low but still somewhat excessive speeds. Within the environment of a factory or similar workplace, such operation is hazardous, incidents of collisions between the vehicles and plant personnel now reaching numbers resulting in a call for corrective action. Speed governors have been considered but rejected, not only because of the complexity and cost of retrofitting existing vehicles with such systems, but also in view of a needed flexibility of speed capability for the vehicles wherein such speeds are made available to the operators for very short intervals or for operation in non-hazardous regions such as those out of plant, for lifting loads and the like. As a consequence of this need for flexibility in operation, it has been proposed that a cuing form of warning be employed with the vehicles to advise the operator that thresholds of acceptable speeds have been reached and further providing warnings to the operator in the presence of hazardous speed. For example, as the vehicle reaches a speed of 5 miles per hour, a light may be energized to alert the operator that the maximum desired in-plant speed has been reached. A next higher threshold of 7.5 miles per hour would represent a hazardous condition warranting a warning provided as an audible alarm such as developed by an energized horn. Should the hazardous speed condition continue for a set interval, for example 3 seconds or the like, then such response as a vehicle shut-down or other action may be called for requiring some form of supervisory notification or intervention.
Because a typical industrial facility will have several makes and varieties of such inplant vehicles, for example having different lifting features, propane or electrically powered motor systems and the like, the cuing systems or devices incorporating such desired features necessarily must exhibit the attributes of universal adaptability and be capable of relatively simple installation procedures. For instance, the systems may gain speed information by monitoring the rotation of the wheel. While a flag or the like attached to a wheel rim readily may be monitored to provide a pulse categorized indication of wheel revolutions, such simple pick-off techniques also may lead to logic error inasmuch as the duty cycle or operating time of the devices involves a substantial amount of stopping and reversing. Thus, the pulse output of such monitoring may contain a substantial amount of false information.
However, while providing a simplicity of retrofit installation, the desired cuing system should provide for possible sabotage on the part of operators. Such sabotage becomes more available as the design for retrofitting the vehicle becomes more simple. An energized horn, while providing a warning to plant personnel that a vehicle within ear shot is speeding, also may be a source of mental irritation to an involved operator posing a temptation to dismantle the device. Thus, supervisory functions should have available some continuum of diagnostic information that the vehicle mounted devices are in proper working order.